Gas cooking appliances, such as gas ranges, often include two or more heat sources or burners for heating a food item contained within an oven cavity of the cooking appliance. For instance, a lower (or bake) burner is often provided at a location adjacent to a bottom surface of the oven cavity for providing heating below the food item contained within the cavity. Additionally, an upper (or broil) burner is often provided at a location adjacent to a top surface of the oven cavity for providing heating above the food item contained within the cavity.
In a typical gas oven appliance, an electronic ignition system is often used to ignite the gas supplied to each burner. For instance, a hot surface or “glow bar” type igniter or system is commonly used to ignite the gas. In such systems, the igniter and gas valve circuit are connected in series. As current flows through the igniter, the igniter heats up. When the igniter reaches a predetermined ignition temperature, the gas valve will open, allowing gas to flow to the respective burner. The glowing hot igniter then ignites the gas flow.
However, if the input power or voltage to the igniter varies or fluctuates, as is common with household electric power supplies, the time required for the igniter to reach the predetermined ignition temperature will vary. For instance, in a typical situation, nominal 120V supply voltages can vary by as much as +10% and −15%. Consequently, it can take on average between 10-50 seconds for the oven igniter to reach the predetermined ignition temperature, open the gas valve and ignite the gas at the oven burner. Such voltage-dependent ignition times introduce significant uncertainty for controlling the heating within a gas oven appliance.
Certain gas oven cooking algorithms typically rely upon timed ON and OFF cooking algorithms, commonly referred to as bake and broil cycles. Specifically, these conventional cooking algorithms providing alternating bake/broil cycles in which the lower (or bake) burner is activated for a predetermined amount of time and, following the expiration of such time period, the upper (or broil) burner is then activated for a predetermined amount of time. The cooking algorithm continuously repeats these on/off cycles such that activation of the burners continuously alternates between the lower burner and the upper burner. However, these timed cooking algorithms are susceptible to inconsistent cooking performance due to the variable input voltages supplied to the ignition system of the appliance. For instance, if the time needed for the igniter to reach the predetermined ignition temperature is longer than anticipated by the timed cooking cycle, the actual cooking time may be adversely impacted.
This is particularly true for the timed broil cycles, which are typically significantly shorter than their corresponding timed bake cycles. For instance, FIG. 1 provides a data table illustrating an example of a conventional cooking algorithm that utilizes alternating timed bake/broil cycles. As shown, the table provides data for ten consecutively ordered cooking cycles, with each cooking cycle including separate bake and broil cycles. Specifically, during the first cooking cycle, the lower burner may be activated for a predetermined period of time (e.g., 200 seconds) and then turned off. The upper burner may then be activated for a predetermined period of time (e.g., 40 seconds) and then turned off to complete the first cooking cycle. Such alternating bake/broil cycles are then repeated (e.g., through cooking cycles 2-10) until the oven reaches the desired temperature.
As shown in FIG. 1, a significant variation in the top-to-bottom heat ratio occurs across the range of input voltages that may be supplied to the igniter associated with the upper (or broil) burner, which may substantially impact the oven's ability to provide even cooking along the top and bottom sides of any food items contained therein. Specifically, for an average input voltage of 120V, the oven achieves a given top-to-bottom heat ratio (e.g., 11.1%), which may, for instance, correspond to the desired top-to-bottom heat ratio for the oven. However, for an average input voltage of 132V, the oven achieves a higher top-to-bottom heat ratio (e.g., 13.5%), which may provide more top-side heating than is desired. Such an increased ratio may result from the igniter heating up to its ignition temperature more quickly due to the increased input voltage, thereby allowing for the upper burner to be ignited or turned on for a longer period of time. Moreover, as shown in FIG. 1, for an average input voltage of 102V, the oven achieves a top-to-bottom heat ratio of zero. Specifically, at such a low average input voltage, the igniter is not capable of heating up to its ignition temperature within the allotted time period for each broil cycle (e.g., 40 seconds). As a result, even though it is intended for the upper burner to be turned on for a period of time during each cooking cycle, such burner is never actually turned on, thereby leading to inconsistent or unbalanced top-to-bottom cooking within the oven.
Accordingly, an improved method for controlling a gas cooking appliance that allows for a more consistent top-to-bottom cooking performance to be provided across a wide range of input voltages to the burner igniters would be welcomed in the technology.